I had the first problem with my ac this week. It was working fine but after 4hrs of running and temps dropping to very cold the fan stopped working. This is an original Armstrong AC. Anyone know of a manual for this unit of repairs? I suspect the ballast went out as the fan barely turns now but is free when I spin it by hand.

Ours did that. I am not a rocket scientist, but without loosing a finger (s) try spinning it once right when you turn it on. The motor up higher is needing to be oiled. Some will tell you the only way to get oil in there is to take the motor off and turn it sideways so the oil will run down in it. But there is an oil called 'Zoom Spout' turbine oil, that you can hold the free moving hose with it - and squeeze as much as you can within reason and then try it.
The other reason may be that the motor is burning out. I have pictures of doing this. PS DO NOT use WD 40 !! It is not a lubricant.